Abstract

Background: Platelet inhibition is necessary in post PCI period as it is one of the risk factor
for stent thrombosis and there are only few studies on platelet aggregation and inhibition
for gender comparison between males and females.

Methods: We have studied 142 consecutive in patients from NIMS cardiology department
from august 2014 to 2016 who underwent PTCA, in the follow up period of 15th day we
did platelet aggregation test for all the patients. We calculated platelet inhibition by 100–platelet aggregation.

Results: Out of 142 patients 30 are females 112 are males. Both the groups are matched in
baseline characteristic of mean age 57 years, hypertension, diabetes, type of presentation (stable or unstable) weight, eGFR, type of stent, presence or absence of LV dysfunction, single
or multi vessel disease. There is significant difference in smoking (p=0.000) between males
and females, and hemoglobin levels (12.12 v/s 13.60 g/dl, p = 0.04) but there is tendency
for higher platelet aggregation (i.e. lesser platelet inhibition) in females, Chi square test
person uncorrected chi square = 1.238, p=0.266,(fisher exact test 2 tailed p value 0.545)
(Odds ratio (OR) = 0.00, 95% CI 0.00 to 6.649 Relative Risk (RR) = 0.00, 95% CI 0.00 TO
5.389). There are 9 (30%) females with higher end on platelet activity >50% in whom there
are nil events in them and there are 24 (21.43%) males with higher end platelet activity
>50% in whom there are 3 non cardiac events ( AV fistula, CSA+CIN, CCF)in them but total
event rate is higher in females(10%) than in males (8.04%). When estimate of difference is
calculated with 95% CI is (-0.125) with test for difference 0 and p value of 0.064

Conclusion: Though there is a tendency of lesser platelet inhibition in female’s events rates
are higher compared to males (10% v/s 8.04%) with p = 0.064 which again shows tendency
but not significance

Abbreviations:

HRPR: High on Treatment Platelet Reactivity

PCI : Percutaneous Coronary Intervention

PTCA : Percutaneous Transluminal Coronary Angioplasty

E GFR : Glomerular Filtration Rate

LV : Left Ventricular

Av fistula : Arterio Venous Fistula

CSA : Chronic Stable Angina

CIN : Contrast Induced Nephropathy

CCF : Congestive Heart Failure

ACS : Acute Coronary Syndrome

DAPT : Dual Antiplatelet Therapy

MACCE : Major Adverse Cardio and Cerebro Vascular Events

CAD : Coronary Artery Disease

CVA : Cerebrovascular Accident

MEHRANS : Bleeding Score

RBS : Random Blood Sugar

LFT : Liver Function Tests

KFT : Kidney Function Tests

ACC AHA : American College of Cardiology & American Heart Association

EDTA : Ethylene Diamine Tetraacetic Acid

LTA : Light Transmittance Aggregometry

PPP : Platelet Poor Plasma

SD : Standard Deviation

Introduction

Coronary artery disease is one of the main causes of morbidity
and mortality worldwide. Throughout the last decade improvements
in the diagnosis and treatment of atherosclerosis have caused a
marked reduction in the morbidity and mortality in men, whereas the
rate of recurrent atherothrombotic events, including cardiovascular
death, in women has increased. As platelet reactivity plays a vital role
in thrombus formation and atherosclerosis, dual antiplatelet therapy
with both aspirin and clopidogrel has become the cornerstone in the
treatment of patients undergoing coronary stent implantation and
those presenting with Acute Coronary Syndrome (ACS). Previous
studies have suggested that women do not accrue equal therapeutic
benefit of antithrombotic therapy. Although multiple contributing
factors have been described, the physiological mechanism behind
this gender disparity remains unclear.

Gender differences in platelet function: Influence of gender
on platelet biology was put forward over 30 years ago [1–4]. Sites of
potential gender differences are in molecular mechanisms of platelet
adhesion/aggregation. Latest works have shown that a gender and
age difference in platelet count significantly (with higher values in
women vs. men and in younger vs. older subjects), and that platelets
in women have a higher number of surface receptors and to bind a
greater amount of fibrinogen [5,3,6,7]. paradoxically females have
higher bleeding tendency over males.

However, some are of opinion that platelet count and surface
expression of glycoprotein (GP) Ib -IX-V (responsible for initiating
adhesion through a von Will ebrand factor) and GP IIb/IIIa receptors
(responsible for initiating aggregation mainly through fibrinogen)
may not accurately reflect overall platelet reactivity [4].

Cardiovascular risk is still underestimated in women though they
are experiencing higher mortality and worse prognosis after acute
cardiovascular events. Cause of Acute coronary syndrome in females
is plaque erosion as compared men where majority is due to plaque
rupture which is nidus for platelet activation. Gender differences are
seen in thrombotic and hemorrhagic risk during Dual Antiplatelet
Therapy (DAPT), thus suggesting a potential variability in platelet
reactivity according to sex.

Women are generally less represented than men in cardiovascular
trials for reasons that include:

Underestimation of cardiac risk due to atypical nature of angina,
misinterpretation of symptoms, biased referral for cardiac
testing, lower rates of appropriate diagnosis or treatment
and lesser rates of referral to coronary angiography for acute
coronary syndromes (ACS) [9].

Lower prevalence of cardiovascular diseases in women below the
age of 65. On the other hand, women included in antithrombotic
drug trials are on average older and have more comorbidities and
risk factors than men, and are thus at a higher risk of adverse
outcomes, including thrombotic and bleeding events [10].

Moreover, because women are more prone to bleeding
complications than men owing, to lower body weight, lower
glomerular filtration rates, and more frequent overdosing of
antithrombotic drugs, the net clinical benefit of antiplatelet
agents tends to be generally smaller in women than in age-matched
men [3-5]

Evidence that gender differences play a role in platelet reactivity
was first reported over 30 years ago and this observation has been
confirmed in many studies.

Compare the MACCE Between the Studies: Differences in
vessel wall biology between men and women, as well as the direct
influence of sex hormones (oestrogens, progesterone or androgens)
on platelets or their indirect effect on the vasculature, might be
underlying conditions from a biological point of view.

Since platelet reactivity plays a pivotal role in thrombus formation
and atherosclerosis, dual antiplatelet therapy with both aspirin and
clopidogrel has become the mainstay in the treatment of patients
undergoing coronary stent implantation and those presenting with ACS. However, both drugs result in a wide interindividual range in
platelet inhibition and the association between high end treatment
platelet inhibition and the occurrence of adverse events is well
established.

Therefore, the aim of the present study is to compare the
magnitude of High on-Treatment Platelet Reactivity (HRPR) between
genders in patients on dual antiplatelet therapy undergoing elective
and emergency coronary stenting and their correlation with MACCE.

Aim & objectives

To see the affect of gender on platelet reactivity and there by
complications associated with lower platelet inhibition.

Methods

Population and study design: This study was a retrospective,
observational study including 142 patients with established coronary
artery disease scheduled for elective and emergency coronary stent
implantation.

Inclusion criteria: All patients with CAD who are undergoing
stent implantation for elective and emergency indications from
AUG 2014 to AUG 2015

Exclusion criteria:

Patients who have not given consent and who does not want
to participate in the study

Who does not want platelet aggregation at 15 days of follow up

longevity less than 1 year

high bleeding risk calculated using MEHRANS score

clinical or telephonic f/u not possible

Tests done

In the present study all patients were on dual antiplatelet therapy
with adequate clopidogrel treatment (defined as a maintenance dose
of 75 mg daily for >5days, a loading dose of 600 mg at least 24 h before
PCI or 600 mg at least 4 h prior to PCI) and low-dose aspirin of 80–100
mg daily for at least 10 days.

The study was conducted according to the principles of the
Declaration of NIMS. All patients gave written informed consent.

Clinical end point:

The clinical end point was a combination of all-cause death, nonfatal
myocardial infarction(defined as the occurrence of ischaemic
symptoms as well as a spontaneous troponin T value or creatine
kinase MB greater than the upper limit of normal),definite stent
thrombosis (according to the ACCAHA criteria) and ischaemic stroke
any other cardio vascular events.

Blood sampling:

Prior to heparinisation, whole blood was drawn from the femoral
or radial vein. Blood samples were collected into Vacutainer tubes
containing 3.2% sodium citrate for all platelet function tests.

Blood samples for whole blood count were drawn into tubes
containing K3-EDTA. Platelet function testing was performed within 2
h after blood withdrawal.

Platelet function testing

Platelet poor plasma (PPP) was used as a reference for 100%
aggregation and maximal platelet aggregation(%) was measured in
non-adjusted platelet rich plasma after stimulation with arachidonic
acid (AA) in a final concentration of 0.5mg/ml to determine onaspirin
platelet reactivity and Adenosine Diphosphate (ADP) in a final
concentration of 20 μmol/L to determine on- ANTIPLATELET DRUG
platelet reactivity

Definition of high on treatment platelet reactivity (HRPR)

It is defined as > 50% platelet aggregation on ADP after
pretreatment with asprin and clopidogrel and the analysis values are
depicted in the (Figure-1)

Statistical analysis

Continuous variables were expressed as mean ± SD, and categorical
variables as frequencies (%). All distributions were checked for
normality. Differences in continuous variables were compared by
independent t-test and Dichotomous variables were compared by chisquare
test

Results

A total of 142 patients who were admitted in our unit in the
department of cardiology were included out of them 112 (78.9%)
males and 30 (21.1%) were females with mean age of 57 years.

They were matched in baseline characteristics like age (mean age 57years) BMI (25 kg/m2), hypertension, peripheral vascular disease,
history of CVA , whether it is single or multi vessal disease, type of
presentation and use of GP2b inhibitor during intervention these
variables are given in Table-1

But there is significant difference in smoking (p=0.00) and
hemoglobin levels (p=0.00) which were significantly higher in males
and high number of diabetes (p<0.01) in females and calculated
CHADS2 VASC scores (p=0.00) were higher in females (p=0.00) that
indicate females are sicker patients and more anemic compared to
males as shown in table 2

LV dysfunction was more in males than females but statistically
not significant.

Mean platelet aggregation in females on 15 day follow up is 42.43
with SD of 24.25 which is higher than males whose mean at 15 day
follow up 31.72 with SD of 20.76 and higher than all cases 15 day
follow up of 33.99 with SD of 21.89

The mean of total distribution 33.99. The distribution follows a
bell curve which signifies there is normal Gaussian distribution.

Females 15 day follow up platelet aggregation has MODE of 49
where as males have a MODE of 19 and all cases have MODE of 25

This indicates females have higher platelet aggregation (HRPR)
and lesser inhibition than males.

Discussion

Women often have been reported to exhibit a higher on treatment
platelet reactivity for both on-aspirin and on-clopidogrel [2]. The
results from the present study support previousfindings that women
have higher end platelet reactivity and a higher magnitude of ontreatment
platelet reactivity than men. In addition, the cut-offs to
identify patients at higher risk of atherothrombotic events as well
as the prevalence of the primary endpoint was similar between
genders. Thus, thepresent study does not support the hypothesis that
higher ontreatment platelet reactivity could account for the gender
differences in clinical outcome and it remains highly questionable
whether this gender-related difference in platelet reactivity has
clinical relevance.

The study has established that patients exhibiting a high ontreatment
end platelet inhibition >50% status has NO higher
tendencyforadverseeventspost-PCI which is in contrast to previous
studies.

As platelet reactivity plays a vital role in thrombus formation
and atherosclerosis, dual antiplatelet therapy with both aspirin and
clopidogrel has become the cornerstone in the treatment of patients
undergoing coronary stent implantation and those presenting with
acute coronary syndrome (ACS) [13,14].

Conclusion

Though there is a tendency of high on treatment platelet reactivity(
HRPR) in females, (10% v/s 8.04%) with p 0.064 compared to males
this is not translated into the clinical events at one year even though
females are sicker patients, there is no correlation between MACCE
and high on treatment platelet reactivity( HRPR). So there is no role
for routine platelet aggregation test in uncomplicated PCI.

Discussion Future Scope

There is future scope for research as the evolution of newer
antiplatelet drugs which have high bleeding tendency and females
are more bleeding risk. Platelet aggregation POINT OF CARE test can
also help solving this issue better

Limitations

We Have Included All Types Of Presentation But Sub Group
Analysis Not Done and Only Concentrated On Gender.